text:
Variable pitch propellers: Why are they constant speed too?
I am studying for my PPL, and after going through aerofoils, lift, drag, optimal L/D ratio, propeller blades and the like, the need for a variable pitch propeller is absolutely clear to me.
It is also clear to me how a variable pitch propeller works, both from an operational and a mechanical point of view.
What I really don't understand is why. What is the basic reasoning behind its implementation?
Why does a propeller have to be decoupled from the crankshaft in the first place? How did we switch from talking about a blade's angle, to caring about its RPMs? If the problem was the blade's efficiency because of its AoA, why are we even talking about RPMs?
Why can't I just have my big simple knob by which I could directly control the blade pitch angle?
Controlling a blade's pitch by its RPMs and manifold pressure, to my very uneducated mind, sounds indeed like a very counterintuitive way of solving a problem.
update
After stumbling on the concept of two-pitch propellers, I managed to find this excellent page which clearly describes the evolution of propeller technology, from the "Ground Adjustable Pitch", to the "Two-Position", to the "Controllable Pitch" (which is basically what I described with my knob example), up to the "Constant Speed" which is an evolution of the latter, for reasons already exhaustively described in some of the answers.

for a slightly different perspective:  direct blade pitch control is the function of a collective in a helicopter.  So it's not completely unheard of, but you still end up monitoring RPM in your feedback loop for the same reasons Peter outlines in his answer.

Sure, you could only fly aircraft with full-authority FADEC systems, only ever fly on autopilot, and never need to know anything about all this stuff. But then what happens if the FADEC or the autopilot malfunction? (Answer, either you crash or you learn how to fly manually...)

A very simple analogy is that a fixed pitch propeller is like a single speed transmission, a variable pitch propeller is like a manual transmission, and a constant speed prop is like an automatic transmission.

@MikeSowsun yes, the question was why does it have to be constant speed

Just as in an automatic transmission, constant speed props are simpler to use and more efficient than having to constantly adjust a variable pitch propeller.

"Why can't I just have my big simple knob by which I could directly control the blade pitch angle?"  You do, it's the blue one!

Note that the earliest variable-pitch propellers weren’t constant-speed. That was a later improvement in usability, efficiency and safety, for the reasons given in many answers below.

The embedded question "why does a propeller have to be decoupled from the crankshaft in the first place?" suggests there is a misunderstanding about how constant-speed propellers work - they are, in fact, rigidly coupled to the engine driveshaft, either directly or through a fixed-ratio reduction gear chain. The propeller/driveshaft RPM ratio is therefore fixed, and the governor of the propeller, in maintaining a fixed propeller RPM, is forcing the engine to run at the corresponding RPM by varying the load placed on the engine.

@sdenham you'rre right, my words were poorly chosen.

A2A's Spitfire for Flight Simulator X has a De Havilland three-bladed two-speed variable propeller. Technically it has 2 speeds, but you can have intermediates speeds. It's very interesting because in this case, you directly control the pitch, not the RPM. I'd strongly suggest playing with that simulation, it will make you clearly understand the limitations and annoyances of such a system.
Basically, everything is possible, but you have to babysit the pitch every change speed changes.

@Salomanuel: "...you directly control the pitch, not the RPM." RPM is just a byproduct of changing pitch - If you change pitch without changing power you will change the RPM. It sounds like in your example the prop is not governed to maintain this RPM with power changes, but that would be the only real difference.

How did we switch from talking about a blade's angle, to caring about its RPMs?

Because of the engine. A piston engine will only run well in a narrow range of RPMs. Going too fast means

lubrication may break down, resulting in excessive wear,
incomplete cylinder filling and fuel burn, resulting in power loss,
increased inertial loads on crankshaft, connecting rods and pistons, resulting in cracks and eventual destruction of the engine, and
Valve float from insufficient valve spring forces, resulting in the piston crashing into the valve heads.

So, clearly, the red line of the RPM gauge should be respected.
Running the engine too slowly is equally undesirable:

Since power is proportional to RPM, the engine produces less power when run too slowly. If you try to force more power from a slow engine, internal pressures must go up, risking to overstress the engine.
There are RPM ranges which must be avoided because of resonance which may eventually result in mechanical damage.

So it is best to run the engine at its specified RPM range (near the red line if full power is needed, a bit less for partial power) and adjust propeller pitch such that power consumed by the propeller equals power produced by the engine. Any difference between both means that the engine will either speed up or slow down!

you beat me to it! -Niels

ah ok.. so it's basically an engineering limitation. I mean, with my hypotetical pitch knob I could easily make the engine suddenly jump well out of its allowed RPM range? So instead of trying to manually adjust for an optimal blade angle, we focus on keeping the engine RPM and manifold pressure under control by changing the pitch angle. If I understood it well.

I wouldn't call it "keep under control", more like "auto-optimize engine power" (or "auto-optimize propellor pitch" if you like to think the other way round). If you'd have a separate pitch knob, you'd constantly have to adjust engine power as to get the best of it. Maybe compare it to a CVT in a car. Where the engine rpm should stay roughly the same because that's in its powerband.

So to flip it around, a motor with a really wide RPM power range (like an electric motor) would not need any prop pitch control, it would just change the engine RPM for simplicity ?

@Criggie: Potentially, yes.  And on the flop side, constant speed is even more important for turboprops than for piston aircraft, since a gas turbine's powerband is even narrower than a piston engine's.

@ontrack: If one had a propeller pitch-control knob, but engine throttle was automatically controlled to maintain constant RPM, how would that differ from having a manual throttle and automatic propeller pitch?  I'm guessing having the propeller adjust pitch based on RPM was simpler than having a mechanical linkage to set pitch, but otherwise would there be much difference?

It wasn't meant to say there is a difference, exactly as you say: It is basically the same.

Because engine RPM is the variable in the feedback loop.
If you did have a nice big knob to directly set blade angle, how would you know when to adjust it, to what setting? You would need to have a feedback signal, like IAS, and a graph that indicates knob setting. No way to verify if you have adjusted correctly, and you’d be very absorbed by the process without being able to scan the horizon.
Engine RPM is a good feedback signal because:

the pilot can hear it while still looking outside of the cockpit;
but more importantly, a change in RPM indicates a change in engine torque, which is a direct indication of blade AoA.

So using engine RPM it is simple to build in an automatic feedback loop: if RPM goes up, increase blade AoA until RPM returns to the original set-point.

Thanks, yes I thought about that as well, thanks for pointing out the feedback loop.

Controlling a blade's pitch by its RPMs and Manifold Pressure, to my very uneducated mind, sounds indeed like a very counterintuitive way of solving a problem.

It depends on the problem. And here the problem is keeping the RPM and the manifold pressure within design range of the engine.
RPM is limited because the acceleration of the pistons is proportional to RPM and the engine is only designed to handle so much, and because the propeller is only designed to handle so much centrifugal force. On high-power engines a run-away prop (that went full flat at full power) will destroy the engine in seconds.
Manifold pressure is limited because it is proportional to the pressure inside the cylinders and the cylinders are only able to withstand so much. If you exceed it, the cylinder heads will break off. And large supercharged engines can go way over MP red-line on the ground at full throttle.
So controlling the engine by the two main limiting parameters seems the optimal way of solving the problem.
And since the manifold pressure is roughly proportional to the torque (well, if you ignore leaning out; leaning out reduces the pressure in the pistons, and thus power, but not manifold pressure), and power is torque times angular velocity, these two parameters also come as close as practical to telling you the engine power.

Thanks for your answer, it helped.

How does having the pilot control throttle and an automatic mechanical system control blade pitch compare with having the pilot control blade pitch and a mechanical speed governor control throttle?

@supercat Directly controlling the pitch and using governor for the throttle is used for helicopter rotors. It provides immediate lift response unlike the throttle/power that for turbocharged and turbine engines has noticeable lag, but it only works that way because significant energy is stored in the rotation of the rotor so the rotor speed only changes a little before the engine catches up.

@JanHudec: I hadn't thought about the effect of a turbocharger, but I can see how one could create a disastrous scenario in manually-pitched-controlled plane.  If quickly adding pitch causes rotation speed to fall to the point that the turbocharger loses effectiveness, the engine might not be able to get back up to speed, even with wide-open throttle, unless or until the pitch is dialed back.  If one quickly added pitch because of a sudden need for power, this could be very bad.  Rotational-speed-controlled propeller pitch would take care of that scenario automatically.

The AoA of a prop's blades depends on both their pitch and the prop RPM, relative to true airspeed.  You're carving a screw through the air some amount faster than the plane is actually going.
When you say "why are we even talking about RPMs", I guess you mean why are we talking about keeping it near-constant?  Or building a feedback loop to make that happen?
If it wasn't kept near constant, we'd definitely still have to talk about it, in connection with appropriate settings for prop pitch, to maintain a good AoA for the blades at various true-airspeed and power settings.  (Where needed power varies as you climb or descend, and with drag which depends significantly on indicated airspeed.)
And that's of course assuming that we had an engine that could produce the desired power across a range of RPMs, or the extra weight of a multi-speed or continuously-variable transmission like you need in a car where constant wheel-speed isn't an option.  We don't have that with internal combustion engines, as some other answers explain.

For the same reason that your car has gears. Why can't you just put your car in first and drive at 70mph with your engine running at 50,000rpm? Or put your car in top gear and pull away from stationary?
In a car, an automatic gearbox does that for you. But you're basically driving a stick-shift here, so you need to do it yourself. Just that instead of fixed 4 or 5 gears (and neutral) to choose from, you get to dial it in more accurately.

Actually directly controlling the pitch would be like stick-shift—accelerating increases the engine RPM and you have to adjust it back by shifting. Constant-speed prop is the aircraft equivalent of a perfect automatic variable-speed drive. And the prop lever is basically equivalent to the lever switching sport or economy mode—keep higher RPM for more power in sport mode, or lower RPM for better fuel economy. Some modern aircraft like the PC-12 even don't have smooth RPM, just the two settings for max power and economic cruise.

In my opinion the most accurate answer. And I would add race cars have a bit more gears than common cars because they are more optimized.

This answer addresses the need of a variable pitch propeller, but does not explain why it should also be constant speed, i.e. why it must be done using RPMs and manifold pressure and not by directly changing the AoA like a "Controllable Pitch" propeller.

@user815129: You misunderstand the answer, it does say the rpm is constant for the same reasons a car engine works in a very narrow range of rpm. The very root cause is engines have torque and power curves with maxima, and therefore they are used at these specific rpm, else you would burn a lot more fuel and could not obtain the full power/torque. That's true for a car and true for a plane. You can read more here.

Why can't I just have my big simple knob by which I could directly control the blade pitch angle?

For operating the aircraft, how would that help you?  What pitch would you want at any particular flight phase?

Controlling a blade's pitch by its RPMs and Manifold Pressure, to my very uneducated mind, sounds indeed like a very counterintuitive way of solving a problem.

What problem are you trying to solve?
For many flights, you want to run the engine at a known power setting (especially during cruise) and at an efficient RPM.  The prop control allows this to be dialed in and maintained over a range of flight conditions.  The specific blade angle that supports those two may vary depending on the conditions.
So if you had a "blade angle" control, you'd either need additional information and more calculations to find the desired angle, or you'd need to optimize for some other parameters to use it.

For what it's worth:
I recall my father's Piper Cherokee Six D 300. It had a constant speed prop; the throttle quadrant had three controls: throttle, mixture, and RPM.
During start-up, taxi, take-off, and initial climb-out, the RPM lever was always set fully forward (max RPM). The prop would, for the most part, go to and stay at its fine pitch limit because ground operation never called for enough power that the prop would need to coarsen the pitch to load up the engine. The exceptions were during run-up checks when a checklist item was to cycle the RPM lever (cycling the prop into coarse pitch) and it seemed during take-off when the advance to full throttle was accompanied by engine rev-up to an RPM which, once achieved, didn't change with increasing airspeed or pitch attitude.
After climb-out, when engine power was reduced, the RPM lever was also backed off to achieve a cruise or cruise-climb RPM.
As power was reduced for descent, the RPM lever was usually put full forward again. This was mostly to simplify power management - in the same way the mixture control was usually set full-rich while not in cruise.
This should illustrate a few key points:

At low power settings, with the prop at its "fine" stop, the engine is basically following a power/RPM curve just like it would if turning a fixed-pitch prop, and that's OK because there's no great demand on it, and the thrust it generates is all you need for taxiing.
At full throttle, there is an optimal RPM the engine should be run at (as explained in another answer). Since this is the maximum RPM the engine should ever be run at, the prop should be calibrated for this RPM at its forward stop.
At cruise, throttle is reduced, so RPM should be too (again, there is an optimum). Since the aircraft is moving through the air at speed, prop pitch needs to be increased so that the selected engine power is applied at that reduced RPM.


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Can engines with a fixed nozzle in the angle of attack have the same effect as the thrust vectoring?

If the figure above represents a missile at the angle of attack and we vector resolution the thrust output from the nozzle, we can see that the thrust is divided into sine and cosine parts. Does the cosine and sine section of thrust cause torque in the rocket about cg? does the cosine part produce nose down pitching moment ?
Edit: In the figure above, sine and cosine are named oppositely

"does the cosine part produce nose down pitching moment ?" -- why wouldn't that be exactly cancelled out by an opposite pitching moment from the "sine part"?

I think the answer to your question is no, the vector sum of the two components is along the axis T of the rocket.

This NASA page should be helpful

@quiet flyer because the distance between sine part to cg is larger than cosine part .

@sophit in nasa page sine component of drag produce restoring moment about cg

That NASA page is confusing.  They ought to clearly state that the aerodynamic stability dynamics are not changed in any way depending on whether the engine is producing thrust or not.  Why introduce the three different cases if they are actually all identical in terms of the aerodynamic torque produced by a non-zero angle-of-attack?  If they are trying to highlight that it makes no difference whether the rocket is producing thrust or not, they ought to clearly bring that out, such as by keeping the AoA same in all three cases and only varying the thrust.  I give the page a failing grade!

@alizera look at this way-- any stabilizing or destabilizing contribution of the motor thrust will be the same regardless of whether the rocket is in the atmosphere or not.  If a rocket tended to stay "on course" just because the motor was thrusting, the dynamics of space flight would be a lot simpler-- no special guidance systems would be needed for any portion of the flight where the motor was firing, regardless of whether the rocket were in the atmosphere or not--

@alizera re "in nasa page sine component of drag produce restoring moment about cg" -- not the sine component of drag-- the whole drag vector.  Because it acts parallel to the flight path, and therefore not in line with the CG.  What does that have to do with the thrust vector and whether it does or does not produce a torque?

(Plus there's the whole other issue of whether we should choose to show the Drag vector as acting at the CP, or as acting as the CG but also accompanied by an aerodynamic pitching torque or moment.  Both are valid, but different.  We come to the same conclusions in the end either way.)

The pitching moment from thrust vectoring comes from the trust axis' position relative to the center of gravity of the rocket or aircraft's body.  If the rocket motor, or jet engine, is rigidly attached to the body, and the extended line of the thrust axis passes through the body's C of G, there are no rotational moments.
It doesn't matter if the rocket motor is at the front, the back, or on a boom 50 feet ahead or behind. What matters is whether the thrust line passes through the C of G.
Thrust vectoring, by gimbal mounting the rocket motor, or using a vectoring nozzle on a jet engine, moves the thrust line to impart rotational moments about the C of G.

so in aircrafts why front prpoller engine mounted cause distablizing moment avout cg at angle of attack ?

@alireza -- are you sure it does?  Are you talking about something like P-factor-- in that case the thrust line does not pass through the center of the prop hub and therefore is not in line with the CG of the aircraft.  But there's no direct equivalent of P-factor as long as far as pitch dynamics are concerned.  Maybe you need to ask a new question about that, if you can sort your thoughts out well enough to ask a clear question --  of course there are effects related to propwash over the horizontal tail, but I don't think that's what you are asking about--

@alireza you have all kinds secondary effects once you add wings, tail, spinning propeller, etc. As far as the thrust force itself goes, that's how it works.  Ppl think jets with tail mounted engines are destabilized by the location of the engines at the back. If the engines are rigidly attached, it makes no difference where they are.

@quiet flyer Yes, the professor of the dynamics and control(flight mechanics) course of the University of India said that if a propeller engine is installed in front of the plane, it will cause longitudinal instability and cause the neutral point to move forward and decreace static margin

@quiet flyer I am not talking about the p-factor. What was explicitly said was that if a propeller engine is installed in front of the plane and the plane is at the angle of attack, the propeller will produce a vertical force, which is the cosine part of the thrust, and because this vertical force is ahead of the cg , it will cause
longitudinal instability.

@alireza If it's moving the NP, that's the surface area of the propeller and spinner in profile having an effect, as if the prop was stopped horizontally, adding its footprint to the airplane's horizontal footprint. If the thrust line passes through the vertical center of mass, thrust does not impart a pitching moment; it's the same whether the prop is on the nose or tail. What does impart a pitch change is increased flow over the tail when power is changed, reducing trim speed for power increases, and increasing it with power reductions.

@alireza -- Re "What was explicitly said was that if a propeller engine is installed in front of the plane and the plane is at the angle of attack, the propeller will produce a vertical force, which is the cosine part of the thrust, and because this vertical force is ahead of the cg , it will cause longitudinal instability." -- then he is simply teaching things that don't make sense.  The logic here is not correct.  If there is such an effect, it is happening for some other reason.

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What are some possible uses of a Data Scientist in an Aerospace Engineering team?
Apparently, data science can be applied to the Aero industry, but how is a question that I still can't find an answer, and which proves to be incredibly elusive online.
I don't mean the Business Intelligence positions, I want to get more involved with the engineering team, working on the products themselves (airplanes, rockets and satellites). I think GNC (Guidance, Navigation and Controls, also called AOCS for sats) is interesting, but I don't want to limit myself to that. By "engineering" I mean working in the design phase of the product itself, rather than with post-market features (such as maintenance prediction).
Can a Data Scientist be useful in engineering, even without much domain knowledge?
Is there anyone familiar with this world that could provide some insight? Thank you

Or a FOQA analyst.  (Somebody with the time to explain what that is can flesh this idea out into a full answer.)

This is a very speculative question. I don't see what you can get here you can't get from a simple search, that is opinions. Data science, ex big data, ex analytics, ex business intelligence, ex statistics, is not always what is expected by data scientists. As of today this is often a buzzword for the customers. That said: A day-in-the-life of an Airbus data scientist

By "engineering team" I mean any team what works on the product, rather than on business intelligence. It could be Navigation, Aircraft designer, Manufacturing, etc. Anything that directly impacts the product itself.

@ymb1 I have added a little more detail in the question. I just want to know what kinds of applications someone with a Data Science skill set can have. If I had to choose, the GNC engineering team sounds really nice, but I could accept to work anywhere.
By "engineering" I mean working in the design phase of the product itself, rather than with post-market features (such as maintenance prediction).

Voting to keep open - Not an opinion but a fact that aeroplane design requires availability of data. The question is particularly about aviation: aircraft-design is the label with the most hits. I understand the question as is, does not need any additional clarity for me.

I'll try to give you my perspective on working in aerospace product/systems development. First, there's no single answer that's all encompassing of the potential scope of jobs in the industry. In a company with a thousand engineers, there's probably 600 different job descriptions.
As an Aero engineer starting out, I had a view of where my career would go. The reality was pretty much something entirely different. The reality is that college taught me some basics, but what was important was how to learn, the scientific method, and how to solve problems. Engineering is just solving problems.
I've worked space systems, avionics, and weapon systems. After that, I moved into civil aviation avionics, mostly comm, nav, and surveillance. I knew development process, I had to learn the technology on the job. Along the way I was on occasion a manager.
As a manager I had to hire systems engineers. There were other managers hiring software engineers and EEs (digital design, RF design, power, etc.) and mechanical engineers (packaging). When you recruit, it's great to find 'the perfect fit' but they almost never exist. So you look for the skills necessary to do the job.
If you were to read the job postings, the would typically say: Systems engineer, must have a Bachelor's degree in engineering, physics, or mathematics from an ABET accredited university. And the it will talk about skills needed for the job (and a description of the job.) I should also point out there a number of jobs in the engineering team that don't have the title engineer. There are Analysts, Developers, Architects. A lot depends on HR decides to classify positions.
If it's a junior level position, under 5 years experience, I'm hiring based on what a coworker coined the Three "A"s - Attitude, Aptitude, Ability, in that order. Attitude is everything. I can't fix that. Aptitude is is important as they'll need to learn. Ability is good, but if they have the first two, they can learn.
Very few will have the perfect background. At higher experience levels work history is important, but I almost never had an exact match. Some did development in a non-aerospace business, others had the degree and some non-related aviation experience. So even here the 3 "A"s apply.
So the answer is read the job postings and figure out how your skills align with those listed and try fill the gaps. One quick way to gain a good basis in aviation is to take private pilot ground school. Actual flying lessons will help, but ground school will introduce you to the aviation world. And then go for it.

I am an aerospace engineer in a drone company and part of my job is "data science".
We have a lot of flight logs on our server, which are uploaded automatically after a flight was done. I am using these as one part of my data source. Other sources can be simulations and specific component tests. As you can see there is a lot of data avaiable, even at our small company. With this data it is possible to improve the flight model (System Identification), improve the controller or create an AI e.g. for remaining flight distance estimation. Also finding out if the health of the Sensors degrade or the servos arent working properly is one part of this. Of course there is much more which can be done. But commonly we are using Data Science as a tool to improve our "aerospace"-functionalities. Data Science helps therefore to improve the understanding of our system.
At least at my job domain knowledge is very important. Knowing how to calculate Coeffcients or knowing which parameters influences e.g. Power Consumption is crucial.

Interesting to hear. My problem would be the lack of domain expertise though. Are there any Data Scientists that work with you that do not have background in Engineering?

@temporario1001, my questions back to you would be: Are there any data "scientists" who have do not have a background in anything except "data"? Generally scientists have a background in the specific discipline they are practicing science in, right? Wouldn't using the scientific method on data then just be one of the functions of doing research in that particular field of expertise? (rendering the researcher a "scientist"...)

@MichaelHall That's a very good point. I mean that I don't have a background in Aerospace Engineering, but in Physics, which is not directly applicable to AE jobs. So I guess the most useful thing I have to offer is Data Science skills.

@temporario1001, I worked with a fellow program manager in an aerospace electronics company who had a degree in physics.  Sometimes you just need to get your foot in the door to eventually get to working at something that interests you.

I think the dilemma in your situation is, that pretty much any engineer is a data scientist in some sense, as engineering deals with gathering information, analyzing it, making conclusions and then advancing design of doohickeys and whatchummacallems.
Airspace engineering requires a lot of specialized knowledge, and thus a sole training of data scientist most likely won't cut it. Data science as such is (according to my understanding) at its best when large sets of data or information need to be dealt with. And by large I mean stupid large.
I'm not sure if even the largest airspace entities have enough such projects to justify employing a data scientist, it may very well be a better option to subcontract this on project bases.
P.S. speculative answer, may get deleted, read quickly

Yes data scientists have a place in aerospace design engineering, as aptly demonstrated by Torenbeek, Synthesis of Subsonic Airplane Design. A treasure of statistical design information. We went through a pre-design process at uni, using the book as a design tool.

For instance the table above, one of very many, lists design parameters for the initial phase of an airplane design. Data of existing planes will have to be explored for a new pre-design, not only geometrical data of course: fuel burn, range, payload, weight prediction, drag calculations etc are all initially determined from statistical data.
The table above was used in this answer, which contains a further example of data analysis from this report, Aircraft Drag Polar Estimation Based on a Stochastic Hierarchical Model. Yes, please read Fowler flaps for Flower flaps.
Data science has a very large role in aeroplane design. Without it, the design would be multiple times more difficult.

could you fix the second link? The one with the answer to another question? It is currently linked to the image of the table you provided.
Also, this seems very interesting, but I am afraid it will require domain knowledge, which I don't have a lot of yet, and therefore it will be out of reach for "pure" Data Scientists. Am I correct? I have a background in Physics, which is not applicable to aviation. Thanks a lot for your reply though, it's really helpful.

Fixed the link, thanks. Yes obviously domain knowledge would be required, should not be a problem to obtain with a physics background.

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When on VFR flight following into a Class C airport, is it typical to cancel before arriving (as with Class D and uncontrolled airports)?
student pilot here getting close to my PPL checkride.
I've flown with flight following into and out of Class D airports before, including on my solo XCs. Every time I've gotten flight following, I've either cancelled it myself when nearing my destination, or ATC has terminated it.
I was just wondering if this is what usually happens at Class C airports as well, or if it's more common in Class C for approach to hand you off directly to tower without terminating radar services.
If I was talking to the Class C approach facility, it would seem silly to cancel flight following myself (as I usually do when approaching a class D destination), since I would then presumably need to contact them again in order to enter their airspace. For the same reason, will they typically avoid cancelling on their end?
Thanks for any insight, and I recognize the answer may well be "it depends."
EDIT: Actually, I think I'm probably able to answer my own question. Since, by definition, you're always receiving radar services when operating within Class C, it effectively makes no difference whether you got in there under flight following, or just cold called approach as you got close. Once you're within the airspace, there's really no difference between being on flight following or not - either way they can give advisories and instructions and will eventually hand you to tower. So I imagine they would never say "radar services terminated," because they're not terminating them.
Would still like to make sure that's correct before "answering my own question," though!

Your edit is correct—it would make no sense for either you to request, or the controller to initiate, termination of radar services. Answer your own question and I will happily upvote it!

There's no reason for you to terminate flight following, or any other radar service, no matter what the class of airspace. The service is there to help you, I'd leave it up to ATC to terminate it.

Thanks to commenters who confirmed my edit is correct, and that the answer to my question occurred to me shortly after I posted it:
Radar services continue by definition through Class C. All VFR aircraft are essentially automatically on "flight following" within the airspace.

While you're at, look up the difference between "Class C services" and "basic VFR radar services." If the AIM or P/CG don't lay it out explicitly, Chapter 7 of the 7110.65 will.

Don’t cancel VFR Flight Following yourself unless you truly don’t want it anymore.
If you’re arriving at a non-towered airport, or at a towered airport without a radar display, then Approach/Center will terminate radar services for you at an appropriate point. For a towered airport, this will usually coincide with a cold handoff: “squawk VFR, contact Tower on xxx.xx”. You will need to give the Tower your position since they’ll have no idea where you are.
If you’re arriving at a towered airport with a radar display (some D, all C and all B), then Approach/Center will give you a radar handoff: “contact Tower on xxx.xx”. Since they can see you on radar, just check in with your altitude, same as any other radar handoff.

Thanks for the answer. My home airport is a Class D with radar, and if I recall correctly, on one of my dual XCs, my CFI and I cancelled flight following on the way back in. I'll try to remember to ask about that, whether it's some local best practice, something we just did for the sake of the lesson, or whatever!

@EthanB Maybe your CFI learned at a tower without a radar display, or at a non-towered field? These nuances aren’t something that is covered at most schools.

If you're landing at a non-towered airport and receiving VFR F/F, as you start your descent it is helpful for you to cancel F/F with ATC before you descend below radar/radio coverage. The controller generally knows when this will happen, but if occupied with higher priority duties, may not realize you're altitude until both radio/radar are list, then we have to treat you as a possible aircraft accident.

@RetiredATC I always advise beginning my descent for exactly that reason. If they choose to keep me (and there are valid reasons to sometimes), it’s on them to remember.


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Will a jet flown on a parabolic arc reach its highest altitude on a warm day or a cold one?
In level flight, on cold days jet-powered planes can fly higher because the air is denser. However, at the same time the true airspeed is lower because of the denser air.
At warmer temperatures a plane accelerates to a higher airspeed, and as a result the higher speed could allow for enough initial speed to reach higher peak altitudes when flown in a steep parabolic arc.
Can a (military jet) plane fly higher in a parabolic flight when the air is warmer?

Interesting question! I reworded it to make it clearer, let me know if this still captures your intent. BTW, is it true that planes accelerate more quickly when the air is thinner? I would have thought the opposite, since there is less oxygen. And did you mean higher delta-v, or higher kinetic energy?

@KennSebesta You're right as technically the plane's delta-v is always the same, I rather mean kinetic energy, I clarified that. Rather than accelerating more quickly the plane reaches a higher true airspeed than at colder temperatures (but this goes hand in hand), and I think it really works, higher apogees can be achieved. The reason the plane goes faster is the warm air which is less dense so there is less air resistance I guess.

This is a very interesting questìon, and not a trivial one to answer. Yes, in hotter air TAS is higher, but how about engine efficiency? And how about lift, which is also imperative when considering flying parabolic, (but not ballistic) trajectories.

@Jpe61 Um, wait, what's the difference between parabolic and ballistic trajectories? My question is concerning those that fly as high as possible, with a high pitch, to altitudes 110~130,000 ft where air is near vacuum.

Strictly speakin ballistic trajectory is "the path of an unpowered object, as a missile".

@Jpe61 Since the plane is entering near-vacuum and eventually floats on inertia only, I'd say it's a parabolic-turned-ballistic trajectory.

Yes, but what I'm after is, that since the question is about a military jet, the procedure would be a zoom climb, so all kinds of aerodynamics are involved. Or are you asking specifically about the portion when the jet is already in the ballistic phase of flight?

@Jpe61 Um, I dunno. The entire flight pattern I'd say. Or rather the initial horizontal flight before starting the zoom climb. E.g. in cold air the plane cannot gather enough speed (or only after a long time) to eventually reach an apogee as high as in warmer air I guess, because when it's cold the denser atmosphere means more air resistance so that in warm air you can fly faster, that's how I understand it if I'm correct.

The maximum airspeed of any aircraft is determined by thrust and drag$^1$.
At first glance it would seem lower density of warm air would favor faster true airspeed (more kinetic energy to climb), but (for airbreathing engines) one can consider the effects of warmer, less dense air on thrust production as well.
Jet engines rely on delta temperature by combustion of fuel to produce propulsive thrust through the expansion of gasses, just like their piston cousins. Therefor, colder air gives them a double advantage of more oxygen to burn and greater delta T.
This is why airliners like to fly in the Tropopause, a region in our atmosphere that is always very cold.
Very luckily, for our parabolic endeavors, the atmosphere warms (and thins) above the tropopause, favoring maximum altitude during the ballistic phase of flight.
Analysis of the flight profiles of the NF-104 and the F-15A "Streak Eagle" show a very similar approach, using maximum thrust to go supersonic in the tropopause, around 6-8 miles high, before angling upwards.
But we must remember to think vertically and have temperature data from all levels of the planned flight.
One other thing about a "cold day" on the ground is that pressure actually drops faster with altitude, enough to cause significant altimeter errors in extreme cases.
So, with the Streak Eagle, they did it on a very cold day.
$^1$ and  structural strength to handle that speed

Pressure drops faster with altitude on colder days?

Yes, and if it got much colder air would be a puddle on the ground.  It's "pressure drops faster with altitude".

In other words, e.g. FL300 above the poles is at a completely different absolute altitude than above the Sahara desert?

I have heard the stratosphere can be as low as 25,000 feet at the poles.

Yes that's true (I even mean to have heard 20,000 ft) and at the equator the tropopause can be as high as 70,000 ft, but these values are about where the temperature stops decreasing, and where it starts rising again with altitude. This doesn't have to do with pressure directly, but with temperature and how high cumulonimbus clouds can go.

@Giovanni pressure is a function of both density and temperature.  Lift at a given airspeed is a function of density.  Jet thrust is a function of density and delta T.  They are all related in the formula PV=nRT.  So you have a taller stack of warmer air to have the same ground pressure.

Why is a greater delta T an advantage? Wouldn't more uniform temps throughout the atmosphere be more advantageous to a plane? The temp of the lower stratosphere isn't a constant minus 56.5°C, it changes with sea level temperature too.

Greater delta T is an advantage for the the jet engine.  You are right about less dense air (warm) being easier to fly through.  Once in the ballistic phase it would be an advantage.  Under power, greater engine efficiency makes it better to be in colder air.

Then it's not a double advantage as you write, because the greater delta T provides for more oxygen and thus for more engine efficiency, so it goes all hand in hand.

The second advantage is greater expansion of gasses.  That's what I mean by delta T.  A third advantage is that aircraft can fly at a lower AOA in denser air for the same lift.  So it is really very complicated.

The tropopause (in the way you mean it, lower stratosphere in fact) actually extends from 7 to 12 miles (11 to 19 km) before temperature starts rising with altitude again. At 45th latitude of course; on the poles it goes lower and on the equator it goes higher. Airliners fly on the lower edge of the tropopause or even below it, the Concorde flew on its upper edge. On a flight from Europe to America I've flown at an altitude of 30,000 ft which is below the tropopause at 45th latitude, but we flew above Greenland so the temperature remained constant, we were in the tropopause/lower stratosphere.

Amazing I learn a little bit answering too. Appreciate that.  I would recommend modeling based on density altitude.  Since atmosphere is not a closed container, pressure differences result in wind flow.  For a given pressure, aviation generally deals with variations in Temperature and Density (rho, literally molecules per volume).  The aircraft must be strong, light, and powerful, striving to hold lowest drag AoA all the way up (while still maintaining adequate lift).  A supersonic jet will also have issues slowing through the drag peak at transsonic.

But since density is dependent on temperature and pressure altitude is universal regardless of temperature, it is good imho.


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What's the optimal zoom climb angle for a fighter jet to reach its highest possible altitude in a parabola?
If a supersonic fighter jet wanted to reach the highest possible apogee it could in a parabola, what's the optimal pitch angle to do so? A too high pitch may result in insufficient thrust and a sooner stall while a too low pitch may result in lower altitudes than could be reached. But I don't think 45 degrees would be the optimal angle because some rocket planes ascend at a higher pitch, right (my question is on jet planes, however)? Or does it mostly depend on the plane in question?

A recent analysis [The symmetry of the Paris gun: when theory is foiled by atmospheric effects  Physics Education, July 2019] of the WW1 'Paris Gun' points to an optimal firing angle for maximum range of 52,7º. Of course, this is not for maximum shell altitude, for which the best angle would have been 90º...

@xxavier Interesting.

This is a high school physics or trigonometry problem; it's not really even about aviation per se.  I think the core question, however, is intended to be about zoom climbs rather than ballistics.  If this is true, please [edit] the question to clarify that's what you're talking about.

@ZeissIkon I rephrased the question a bit, but I made clear it is concerning air-breathing jets before already, hence it belongs to aviation imho.

Much clearer what you're after, and it no longer looks like a high school problem.

@ZeissIkon The thing is, above ~90K ft (27 km) aerodynamics essentially stop applying and you're being carried by momentum in free fall on a ballistic trajectory, as was the case in Aleksander Fedotov's record-breaking flight for instance. Technically it's a suborbital spaceflight, hence I don't quite understand why space is defined at ridiculously high altitudes around 80-120 km. If I posted the question (in its former state) on space.SE they'd tell me it's below the official definitions and therefore off-topic, even though physically there's no difference to SpaceShipOne/Two flights.

By even the old 100 km definition, neither MiG 31 nor SpaceShips One or Two get to space.  Even New Shepard barely breaks 100 km.  Zero gee due to insufficient lift isn't the defining point of space; the old border was the Karmann Line, at the point where the speed for wing lift to support the craft is the same as orbital velocity.  X-15 pilots wouldn't get astronaut wings if they flew today.

@ZeissIkon SpaceShip One did reach 100 km and more. The Kármán line (which isn't definite but dependent on the plane in question and other factors) is unnecessary because no plane tries to fly horizontally aerodynamically at those altitudes. By contrast, orbiting spacecraft reached perigees lower than 80 km and continued orbiting. When I.C. Kincheloe reached 126,300 ft in the X-2 in 1956 he was declared the first man in space.

In general, the highest altitude for a ballistic parabola flight in an air-breathing jet (which will be flamed out for the highest part of the flight, assuming it's the kind of high performance craft like a MiG 31 or F-104 that's usually used for this kind of maneuver) will be a trajectory that maximizes the vertical component of velocity.
This is done with what's called a "zoom climb" in which maximum horizontal speed is traded off for maximum vertical velocity with a pull-up.  Although a simple-seeming maneuver by appearance (and one that dates back to the First World War), this is a complex maneuver to optimize, and is highly dependent on the aircraft type used, because different combinations of airframe and engine have different high altitude speeds and remaining thrust at a given altitude.  The common factors, however, are a near-terminal horizontal sprint, a pull up at a G level that wastes the least energy, and a final angle that gets the most acceleration or least deceleration during the remaining engine run time before flameout due to lack of air pressure to keep the engine running.
As noted, the end goal to maximize altitude (hence zero-G time for the paying passenger, as that's pretty much the only use of this kind of maneuver since the early days of almost-spaceflight) is to maximize the total of vertically oriented kinetic energy and gravitational potential energy at the point where power is lost.  Since the altitude of engine flameout due to lack of air pressure is fairly constant for a given engine, this reduces to maximum upward velocity at flameout.
For the few aircraft types capable of this maneuver (zero-G parabola above flameout altitude), there will be an optimum pull-up rate for each type that gives the highest final vertical velocity, and since altitude is the goal rather than distance, the final angle will be significantly closer to vertical than the 45° for no-drag maximum range, but lower than the 90° for maximum altitude of a purely ballistic trajectory (because the longer T/W can be kept above 1, the more velocity can be kept or built up).
As far as I'm aware, the only aircraft type currently in use for this kind of flight is the MiG 31, a high altitude interceptor originally intended to shoot down the SR-71 (some claim it never came close, some records indicate otherwise).  In additional to high altitude and high speed capability (around Mach 3 at 20 km, give or take), it has a reaction control system that permits maintaining control when the air is too thin for control surfaces to be effective.  The F-104 was capable of this maneuver, but due to lack of RCS as built it was a very dangerous stunt rather than something that could be done routinely.

So the pull-up shouldn't be too fast, instead the pitch should slowly get to more than 45°?

Excessive G increases drag too much relative to lift, wasting energy.  Worse, at high enough G and high altitude, there's a risk of accelerated stall, even at high speed, which (in supersonic flight and extreme altitude) might lead to an unrecoverable condition (flat spin, airframe breakup, etc.).

A good historical reference is the F-15 Streak Eagle flight. The last flight to 30km included a zoom between 30k ft to 40k ft to Mach 2.2 followed by a 4g pull to a 60 deg climb.  The engines flamed out around 60k ft.  Above that it was a ballistic flight where the goal was to maintain near zero angle of attack for minimum drag and to ensure the plane descends in a controllable attitude. There were a lot of simulations run to determine the best flight profile.

There are at least two records of MIG-31 having being in a position to shoot SR-71 down at will. It was, in fact, a successful repellent for SR-71 missions in Russian airspace.

It depends on the plane in question, more specifically the weight, wing, excess thrust, G loading limits, and its Vnever exceed speed.
Looking at the flight profile of the modified F-15 "Streak Eagle" of the 1970s, one can see the technique is to build up as much speed as possible, then try to climb at as high an angle as possible.
The Streak Eagle, stripped of all unnecessary equipment (including its paint), and carrying limited fuel, was able to achieve a thrust to weight ratio of 1.4!  This airbreathing rocket could accelerate in vertical flight!
But the drag of turning to vertical cost the jet precious airspeed (kinetic energy), so the optimum climb angle was around 60 degrees, with the transition from building speed to climbing done at around 30,000 feet, which is above the denser layers of the atmosphere but still allows for aerodynamic manuvering. As the aircraft climbs into thinner air, less oxygen means less thrust available.  The highest altitude comes from the straightest path$^1$ up.
For more typical subsonic aircraft with a thrust to weight ratio closer to 0.25, speed can be built in a shallow dive, but will be rapidly lost in a steep climb.  Their "parabola" will not be much different than the max service ceiling of the aircraft.
In summary, the optimal profile for a given aircraft for a maximum altitude parabolic flight is to climb as steeply as possible as fast as possible from the highest altitude possible with the least amount of drag.  Essentially, at that point, the aircraft is a projectile.
$^1$ this cost General C. Yeager one last bit of glory when the NF- 104 was "pulled up" to increase angle of climb during the
ballistic phase of flight, resulting in a lower apogee (from
increased drag), and a stall.


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Has the infamous Sao Paulo runway been made longer or replaced meanwhile?
The TAM 3054 accident occured because the pilots were stressed by the fact they needed to land on a not-so-long runway where an incident occured a day before. This stress has lead the pilots to forget about setting the thrust levers to idle. The link writes that after the accident the airport used an alternative runway for some time, but what happened to the infamous one? Has the runway been either prolonged (that's probably hard because there are roads in the vicinity) or closed permanently in the meantime or do pilots still have to land on it?

@mins Because of when it's raining, there had been an incident the day before. But this has been dealt with as evident from Bianfable's answer.

The runway has not been extended. The final accident report lists the runway length for 17R/35L (the accident runway) as 1945 m:

It has two asphalt landing-and-takeoff runways: the main runway (17R/35L),
measures 1945 x 45 meters; and the auxiliary runway (17L/35R), measures 1435 x 45
meters.

My current Jeppesen chart for SBSP lists runway 17R/35L at a length of 6365' (1940 m), so basically the same. The other runway (17L/35R) is listed at 4905' (1495 m), so slightly longer.
The runway has however been equipped with rainwater drainage grooves after the accident:

The airport has been troubled by slippery runways and has had several accidents where water accumulation has been a significant factor (most notably, the one involving TAM Brazilian Airlines Flight 3054 in July 2007). Although the main runway was repaved in June 2007, its new rainwater drainage grooves were only finished in September 2007.

(airports-worldwide.com)
Since 17R/35L is still the longer runway, it is obviously still in use today. It has ILS and RNP approaches on both ends, where the shorter runway only offers RNP.


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When did Piccard reach his record altitude of 23 km (75,500 ft)?
Swiss physicist and balloonist Auguste Piccard reached world altitude records of 15.8 km (51,800 ft) in May 1931 and 16.2 km (53,000 ft) in August 1932, accompanied by Paul Kipfer in the former and by Max Cosyns in the latter flight.
The Wikipedia article writes he ultimately made 27 balloon flights and has gone as high as 23,000 meters (75,500 ft). When did Piccard fly to that altitude, and do you know a list of all his balloon flights?
Edit: Above assumptions and Wikipedia claim are outdated now that it's clear Piccard didn't make such flight and the WP article has been dealt with.

On one hand, the answers here are convincing, but, on the other, it seems that we have video of Picard making it all the way into outer space. ;)

@AravTaneja I didn't know either, and he actually didn't go to 75k ft as we found out here.

FYI I have edited the wikipedia article to remove the line about him making 27 flights as I think we have firmy established that it is unlikely to have been true

I strongly believe that the wikipedia author has misquoted a german language reference.
There are many places you can find reference to 25 (sometimes 27) altitude records being made (including Piccard in places), but the August 1932 flight to 53,000 ft seems to have been Piccard's last

The following year, Piccard broke his record with an ascent to nearly 55,000 feet (16,764 m), and within a few years, others had risen to nearly 61,000 feet (18,593 m). Since then, manned balloons have risen to over 113,000 feet (34,442 m)
Emphasis mine, source: https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/auguste-piccard-and-paul-kipfer-are-first-enter-stratosphere

A good breakdown of the 25 significant balloon altitude records can be found on wiki with the relevant section reproduced below.

1931-05-27: 15.781 km (51,770 ft) – Auguste Piccard and Paul Kipfer in a hydrogen balloon.
1932: 16.201 km (53,150 ft) -Auguste Piccard and Max Cosyns in a hydrogen balloon.
1933-09-30: 18.501 km (60,700 ft) USSR balloon USSR-1.
1933-11-20: 18.592 km (61,000 ft) Lt. Comdr. Thomas G. W. Settle (USN) and Maj Chester L. Fordney (USMC) in Century of Progress balloon
1934-01-30: 21.946 km (72,000 ft) USSR balloon Osoaviakhim-1. The three crew were killed when the balloon broke up during the descent.
1935-11-10: 22.066 km (72,400 ft) Captain O. A. Anderson and Captain A. W. Stevens (U.S. Army Air Corps) ascended in the Explorer II gondola from the Stratobowl, near Rapid City, South Dakota, for a flight that lasted 8 hours 13 minutes and covered 362 kilometres (225 mi).
1956-11-08: 23.165 km (76,000 ft) Malcolm D. Ross and M. L. Lewis (U.S. Navy) in Office of Naval Research Strato-Lab I, using a pressurized gondola and plastic balloon launching near Rapid City, South Dakota, and landing 282 km (175 mi) away near Kennedy, Nebraska.
1957-06-02: 29.4997 km (96,784 ft) Captain Joseph W. Kittinger (U.S. Air Force) ascended in the Project Manhigh 1 gondola to a record-breaking altitude.
1957-08-19: 31.212 km (102,400 ft) above sea level, Major David Simons (U.S. Air Force) ascended from the Portsmouth Mine near Crosby, Minnesota in the Manhigh 2 gondola for a 32-hour record-breaking flight. Simons landed at 5:32 p.m. on August 20 in northeastern South Dakota.
1960-08-16: 31.333 km (102,800 ft) Testing a high-altitude parachute system, Joseph Kittinger of the U.S. Air Force parachuted from the Excelsior III balloon over New Mexico at 102,800 ft (31,300 m). He set world records for: high-altitude jump; freefall diving by falling 16 mi (26 km) before opening his parachute; and fastest speed achieved by a human without motorized assistance, 614 mph (988 km/h).
1961-05-04: 34.668 km (113,740 ft); Commander Malcolm D. Ross and Lieutenant Commander Victor A. Prather, Jr., of the U.S. Navy ascended in the Strato-Lab V, in an unpressurized gondola. After descending, the gondola containing the two balloonists landed in the Gulf of Mexico. Prather slipped off the rescue helicopter's hook into the gulf and drowned.[a]

If Piccard would have broken his own record, I'm fairly certain it would have been documented in this list, but as you can see after the 1932 ascent the record was broken by others, with the US Navy breaking 23KM in 1956 - by which time Piccard had long-ago moved on to deep sea descent rather than stratosphere ascent

In the mid-1930s, Piccard's interests shifted when he realized that a modification of his high-altitude balloon cockpit would allow descent into the deep ocean.

Back to my original assertion, the final word will lie with whoever can check the reference from wikipedia:

Dr. Erich Tilgenkamp - Reisen in ungewöhnliche Räume - Eine autorisierte Biographie - Verlag neues Leben Berlin 1956.

@mins interesting counter point. But im not convinced Piccard et al made 25 flights at all - the balloon records list is 25 in total. That to me sounds likea  bit of a coincidence! Which is where I think the misquoting comes in. I think there have been 25 balllooning altitude records set, not that Piccard made 25 flights.

However having re-read that guardian article (I did read it when originally looking up this answer) I find nothing compelling about that evidence. There's no citation, and its typical non-scientific journalism. It's probably quoting wikipedia!!

I knew the flight altitude record list, and this is why I asked this question, Piccard's other flights aren't mentioned there. If he indeed reach 23 km, that record was broken in 1951  by Bill Bridgeman in the Douglas Skyrocket (you have to look at the below list of highest plane flights as well), not in 1956. If Piccard indeed reach 23 km, I wonder if e.g. Osoaviakhim-1 occured before or after it. To me it seems it occured before.

I'm open to being proved wrong but I can find no cited details of these supposed 27 flights Piccard made. Either Auguste, or Jean nor the two combined.

BTW, you can edit the Wikipedia article if you can improve it.  It's a big help as Wikipedia is used by millions of people daily.

@RockPaperLz-MaskitorCasket Including journalists ...

@Peter-ReinstateMonica If only we still had a large cadre of real journalists on our little planet... I think we're down to about a dozen of them.

This is a just barely an answer, but: the most reputable source for any aviation related record is
World Air Sports Federation / Fédération Aéronautique internationale - FAI
Auguste Piccard has two records of records in FAI database (pun intended), one of which is still current:
A-8th   Altitude    15 781 m    27 May 1931 Ratified - superseded since id 10634
AA-14   Altitude    16 201 m    18 Aug 1932 Ratified - current record   id 6590

Now, if Piccard had flown higher in a verifiable undisputed manner, it should definitely show in FAI records. The fact that this is not the case does not exclude the possibility Piccard had in fact flown higher than 16201 meters, but there obviously is no significant proof to support this claim.
Piccard was an established and highly regarded scientist, and his flights were scientific experiments by nature. He did, as a scientist, with great certainty keep strict logs of his flights, and as I understand did not perform these experimental flights alone. So it is likely there was a witness on all flights.  I'm not familiar with FAI requirements for setting world records. It may require more observers, perhaps.
I'm certain he did not "pull his stunts" for the sake of breaking records. While doing his experiments he got high (sorry, thats a lame pun but I'll let it fly), but the records were not the point. That may have been a reason not to seek ratification as world record for possible higher altitudes he may have ventured into.

The FAI is anything but a reputable source. They didn't count any flight in which the pilot(s) left their aircraft on their own rather than landing with it, and they didn't count any flight in which the aircraft was launched from another carrier rather than by itself. That's why e.g. Bill Bridgeman's, Marion Carl's and Arthur Murray's flights aren't FAI records, not even Iven C. Kincheloe's spaceflight. But user mins has lifted the veil, they deleted their comment meanwhile but they post a link to an interview with Piccard which makes clear Piccard didn't perform any such flight to 22 km.

Well that would be a question of categorizing, not reputability (is that a word ). So FAI does not have a category for altitude records where the aircraft is not landed in a controlled manner, I presume?

Right, concerning the pilots themselves. E.g. German Titov performed the then-longest spaceflight in Vostok 2, becoming the first man to stay in space for more than 24 hours. The FAI didn't care because the cosmonauts eject themselves out of the Vostok before its touchdown, so the FAI declared John Glenn in Friendship 7 as staying longest in space (he made 3 orbits). The Soviet Union did the right thing by not participating in the FAI.

Are we to discuss flights during which Auguste Piccard exited his condola? Oh, and pls check your facts, German Stepanovich Titov's flight on august 7th 1961 is listed as FAI world record for both duration (25h 11min) and distance (703143km) @Giovanni

There could have indeed been a flight in which Piccard parachuted out of the gondola (but there wasn't as is now clear). Titov's flight is listed today but things were different in the 1960s.

So you would agree that FAI is a reputable source now? History is fluid.

No, because they still claim "the" Kármán line is at 100 km (62.14 mi) when in fact it's much lower on average. And there's no single Kármán line, it depends on the plane in question. A symposium to revisit the Kármán line should have been held in 2019 but they cancelled it.

Ah. Ok then. You win.

Let us continue this discussion in chat.

@Giovanni: "user mins has lifted the veil, they deleted their comment meanwhile", but the relevant information is not lost, it is part of this answer.


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Why do pilots slowly give the plane more thrust during takeoff?
I have mostly seen pilots slowly pushing the throttle to toga during takeoff. But why? Why don't they just directly put the throttle to toga? Wouldn't that save runway length?

Related: During takeoff, why throttle forward then raise hand from throttle to push a button, instead of pushing button then throttling? and Why should jet engine throttles be moved smoothly?

“Slow is smooth, smooth is fast.”

Until the 1970's fuel crisis changed engineering considerations, most motor vehicles would break traction under heavy throttle or steering. And airplanes have even less traction with the air than do cars with the road.

@dotancohen there are 2 parts to your comment, and I don't understand either of them: (a) ABS, ESP etc. are safety, not fuel efficiency improvements, and AFAIK came around in the late 80s and 90s; (b) "breaking traction" with the air would be something like cavitation in ship propellers? But even if cavitation would be possible in air, I think increasing thrust too fast wouldn't cause it because of the inertia of the turbine?

@rob74: I mean that cars when engineered as simple devices are fitted with tires that have enough traction for most conditions, but can sometimes be overpowered by aggressive throttle and maneuvering. The engineering considerations combine tires with an engine powerful enough to overcome their traction under some conditions. Likewise, an aircraft engine can overcome the limits of the the vehicle's rudder and ailerons.

The engines may accelerate slightly differently, resulting in an asymmetric thrust. Spooling up slowly at first (normally to about 60% N1) prevents this. After that, you can accelerate up to full TO/GA (or press the button) without any significant asymmetry.

A pure engine-side viewpoint:
Engines don't really like their power level being changed quickly. Doing so, one increases the thermal and mechanical stress over the engine parts, as well as the probability of engine failure, unstable operation or flame-out. One doesn't want some of these things happening during take-off.
Aircraft engines are pretty much reliable these days, but one should not expend their luck quota for no good reason.
(These considerations are not limited to aviation, any seasoned truck driver does the same with the throttle pedal unless there is a compelling reason to act quickly.)

Even more broadly, being gentle with machines unless necessary is good engineering pratice

Aircraft turbine engines are reliable these days mainly because there is an electronic control unit that knows how fast it can increase the fuel flow without the engine stalling and slows the advance of thrust if the pilot is too fast.

High-powered single prop planes may react violently if the throttle is opened abruptly. Torque reaction and P-factor should be smoothly dealt with...

This is true, an inexperienced P-51 pilot (he had the money to buy one but didn't get enough training) jammed full throttle on go-around and it flipped the airplane over for a fatal accident.

And smaller planes, like your single engine Pipers & Cessnas, may stall if you just shove the throttle to the firewall.

And even smaller planes like ultralights can really get out of hands if you "floor it". Their power to weight ratio can be crazy. Ask me how I know

...so rather than high powered, I'd say high power to weight ratio...

@Jpe61 How do you know this?

I've tried it. First time in a rotax powered ultralight (Ikarus), I was tad bit too agressive with the throttle, we almost ended up off the runway. The plane will not flip as in the example mentioned by GdD, but it will pull to the side extremely hard. Granted I was not accustomed to the control response either, but the power to weight ratio is quite extreme. After liftoff we would have been able to climb very steeply, SEP's I've been in don't come even close. Instructor adviced to retard throttle and climb out on partial power to keep forward visibility better.

@Jpe61, you were on the ground where the gear provides stability against rolling, while the GdD's example was during go-around, so presumably still in the air where it could roll freely. It's a good argument to do some training on go-arounds so you get the feel how much rudder and aileron you need to add when advancing throttle quickly.

Yes, I fully undestand that. I've heard of flipping ww2 fighters even on ground with "reckless throttle management", although I'm not entirely convinced it is possible. The ultra I flew was quite stable once airborne, there was no chance of rolling it with throttle use while flying, during go arounds or othewise.

My Lancair IV-PT doesn't have enough rudder authority at low airspeeds to counteract torque and p-factor - if you jam the power lever full forward from a standing start you'll be taking a scenic tour of the grass off the left of the runway. You need to gradually add power over the takeoff roll, reaching full power at 60+ kts.

On smaller planes, the way it was explained to me was a mix of letting the engine come up to speed more easily as well as smoothly applying the left turn tendency from the inertial changes from the prop spin.
This left turn tendency is less of an issue on a dual prop plane with counter rotating props, but it's still a lot harsher on the engine and isn't really needed.  If you need maximum power from the start of your take off roll, you can hold the brakes to keep from moving forward until at full power rather than forcing the engine to handle extreme changes.

Smoothly adding power allows the pilot to look at engine parameters as engine increases RPM/N2 and possibly avoid a failure at a critical time. With multi engine aircraft it also avoids a bunch of asymmetric thrust and a possible runway excursion. Our Falcon 2000LXS manual actually recommends advancing the power levers from idle to takeoff power over a 3 to 5 second period.

There is rarely only a single reason for something. In the aircraft I currently fly, there is a dynamic counterweight system in the engine. This system absorbs torsional vibration of the crankshaft in normal running. However, rapid power setting changes can lead to the counterweights "detuning" and causing significant damage to the engine, as well as potentially loss of power.
Of course, if the engine lacks a dynamic counterweight system, this reason does not apply. In general however, most engines will last longer if they are operated with care rather than making rapid power setting changes. For regular public transport, minimising the cost to the company is important for financial viability.

I think you're a tad confused... they don't. Pilots typically push it to full or almost full throttle the second they begin to accelerate for take off. The slow increase you feel is actually not a slow increase in thrust (the force applied to move the plane forward), but the rate at which the heavy plane full of people is accelerating (increasing in speed).
Please remember Newton's second law, which tells us acceleration is Net Force divided by Mass. Massive objects such as a heavy passenger jet (such as a 747, which weighs 183,500kg without any people on it!) would accelerate veeeerrrryyy slowly even with a large force added to move it forward.
We can also use, for example, a muscle car at a drag strip. Why does the driver in the competition slowly push down on the gas? Why doesn't he (or she) just floor it? Well, they're actually adding gas/'thrust'/force very quickly (they have to, to move their heavy cars the entire 1/4 mile so quickly!) but it takes time to take a heavy object and make it go from not moving to moving VERY fast (cars often exceed 100mph by the end of the 1/4 mile, and passenger jets average around 4 or 5 hundred km/h groundspeed).
Hope this helped!

What you feel is indeed a slow increase in thrust, not a slow increase in speed. What you feel is force. You cannot feel speed. It takes a relatively long time (several seconds) for commercial jet engines to spool up, so you do indeed feel the change in force (and, thus, the change in acceleration) as the engine power is increased. You feel it even more in larger aircraft like the 747 you mentioned than in smaller ones, since larger engines tend to take more time to spool up (due to more rotating mass in the engine that has to be accelerated.)

Even on light aircraft, though, we don't just suddenly jam in full throttle. We can add power much faster than huge jet engines can, but we do smoothly increase the throttle to full, not just suddenly jam it full open from idle. Doing that would decrease the life of the engine and aircraft engines are expensive. Also, it would lead to sudden changes in forces (e.g. p-factor) that the pilot would have to counter with other control inputs.

(Also, as a side note, I think you've mixed up your units in the last paragraph. Passenger jets average 450-550 miles per hour ground speed when cruising, not kilometers per hour. Large passenger planes haven't been in the 450-550 km/h range since the before the beginning of the jet age. The Connie was at the upper end of that range, for example.)


text:
Pilot communication with ATC partially unreadable
Can anybody decipher this pilot's landing request due to moderate turbulence (some unreadable words...).   Thanks !
https://www.icloud.com/iclouddrive/03kDM9-xQ7Oyz3kUaeRJj6M5Q#AUDIO-2021-12-03-07-51-16

This is what I hear.
“Boblika tower, Air China Niner Two Niner request”
“Air China Niner Two Niner request to uh climb to eleven thousand six hundred meters due to uhh moderate turbulence”
It is the same person making both transmissions as you don’t hear the tower respond to the first request.
The tower name is most probably incorrect, but if you went through a list of control towers you might be able to pick it out and correct the spelling.
It may not even be a tower that the request is made to. It seems unlikely a tower facility would be controlling flights operating at 11,600 meters, but in Russia or China, anything may be possible.

Sweet. Pretty much a copy of my answer

Thank you very much for helping on this one !   I was understanding a request to land so I was confused with the altitude mentioned,

Thank you very much to both of You, Mike and Jpe, for helping on this one !   I was understanding a request to land so I was confused with the altitude mentioned.   Now, I "clearly" understood that it was a request to climb.  Thanks again !  I'm not myself a native english speaker but was pretty baffled by the pilot's accent !      As for the facility called by the crew, I looked at the planned route of    Air China 929 ( Shangai PVG to Tokyo NRT)  and the associated facilities: I found that KCZ Kōchi airport might be the one called, but the first word of the  pilot comm is totally unreadable.

Anyway, Thank you very much again, as I now understand this communication !    Cheers !

If anybody's interested, here is what OpenAI's Whisper transcription model produces, verbatim:

Air China 939 request to climb to 11,600 meters due to moderate turbulence.

Looks like it filters out the filler noises and pretty accurate.
Here is the Python script:
import sys
import openai

openai.api_key = # YOUR_OPENAI_API_KEY

filename = sys.argv[1]

audio_file = open(filename, "rb")

result = openai.Audio.transcribe(
  model="whisper-1",
  file=audio_file,
  max_tokens=1024,
  speaker_labels=True,
  prompt="Transcribe this airplane communication audio file, differentiate between speakers where possible. Return markdown format."
)

# Save to Markdown file
out_file = filename.replace('.mp3', '.md')
with open(out_file, 'w') as f:
    f.write(result['text'])

print(f"Transcription saved to {out_file}")

Note: I'm not sure the prompt does anything, I tried to get a nice markdown format out of it, but it just produces the plain text. Maybe too short, but would need to try with more files.

I like this answet


text:
What are the best known protections against Lasers aircrew's vision incapacitation during critical flight ops?
What are the best known protections against Lasers aircrew's vision incapacitation during critical flight operations (i.e. landing,take-off,emergency).


text:
By aircraft design, excluding engine power, how do you make planes that have a tight turn radius while maintaining speed?
What are all factors in design, excluding engine power and acceleration, thrust vectoring and flight computers, that makes a plane that have a real tight turning radius while maintaining speed? Like larger elevator, light weight etc. Where should the centre of gravity be placed? What are all aspects I need to know?

I'm not sure we have quite enough information here-- the answer might possibly depend on whether the "power loading" is ample, or modest?

Can we assume you want the plane to turn its path , not just rotate its orientation while moving in a straight line (as modern fighters can do) ?

Can an airplane have one engine in full reverse thrust and one engine in full forward thrust?

In a turn you have two opposing effects: In order to tighten the turn, more of the lift needs to be tilted sideways for the needed centripetal force. At the same time, you want to fly slowly so the turn rate and with it the centripetal force stays manageable.
Starting with the equation for the turn radius:
$$R = \sqrt{\frac{m^2}{(\frac{\rho}{2}\cdot c_{L}{\cdot}S)^2  - (\frac{m\cdot g}{v^2})^2}} = \frac{v}{\omega} = \frac{v^2}{g\cdot\sqrt{n_z^2-1}}$$
you can see that radius $R$ is directly proportional to speed squared for the same load factor. Hence the desire to fly slowly. If you now plot turn radius in a Cartesian coordinate system with speed on the X axis and turn rate on the Y axis, lines of equal radius fan out from the origin like this:

Now there are two boundaries which determine where in this Radius-turn rate relationship an airplane can fly:

Minimum speed at a given load factor (bold green line below), and
Maximum sustainable load factor, which is limited by the structure and engine thrust (bold red line below).

Since compensation of the weight still needs some vertical component of lift (which explains the -1 in the denominator above), the green line creeps up to smaller radii as load factor increases (and the weight becomes less significant compared to the centripetal force). As soon as the airplane flies faster than minimum speed (the area to the right of the green curve), radius suffers.
This means the tightest turns are where the bold red and green lines meet. This minimum radius point can be shifted to smaller radii by:

Lower wing loading. This will allow the airplane to fly more slowly.
Higher maximum lift coefficient, for the same reason.
Higher structural limits, so a higher load factor can be flown.

Of course, it must be possible to power the airplane at the minimum radius point and to trim the resulting pitch speed. Since engine power can be excluded here, the factors which help with a high pitch rate are:

Low natural stability. The center of gravity should only be slightly ahead of the neutral point.
Low stick forces over load factor, if you have manually operated controls.
Short tail lever arm, which keeps pitch damping low.

If you have trouble to achieve enough thrust at the minimum radius point, try to increase wingspan in order to reduce induced drag. At this point induced drag has by far the biggest share of overall drag.

"Maximum sustainable load factor, which is limited by the structure and engine thrust" And also by human biology. Pull more than about 10Gs, and the pilot isn't going to be feeling too good. This is important with high-performance fighter aircraft.

@nick012000 Unless the OP is designing a UAV.

@nick012000 At that g load, your engine will probably quit before the pilot does, if it is a jet. G loads for jet engines are quite strict - small deformations will already cause catastrophic failure.

@PeterKampf The reason they're designed that way is because there's no point overengineering a fighter aircraft to be capable of performing manoeuvres that will kill its pilot, so the fighters are designed to fail at the same time as their pilots do.

@nick012000 As you can see from the graphs, higher gs quickly give you diminishing returns. It is more clever to make the structure less beefy, resulting in lower structural mass and lower wing loading, allowing the plane to fly more slowly. That is the best strategy for tighter turns.

This generally means a short wingspan with an extra-strong wing spar structure (to take the lift and G loads), a wing with either high-lift devices that deploy in the turn or a relatively thick wing profile, no fuel tanks or excess mass in the wing itself (to minimize the axial moment of inertia of the airframe), big ailerons (to generate a large rolling moment), boosted controls (so a human is capable of working those big control surfaces) and a big engine (to maintain altitude & airspeed during the turn).
You'll find most of these design features in an aerobatic plane or a fighter.

In general, keeping mass as close as possible to the centre of gravity minimises the moment of inertia so the control surfaces have less work to do

To be honest, those sailplanes have by far smaller minimum turn radii than any fighter due to their much lower wing loading.

@PeterKämpf, thanks, will edit. -NN

Wouldn't tanks (with fuel in them) in the wings help the wing to widthstand the load factor? Assuming the said fuel would otherwise be stored in the fuselage?

No, and if the wings held the fuel then the plane's roll rate would be slowed.

Stunt plane, +1. Control surfaces almost as stupidly large as its power plant and it weighs nothing.

You specifically talk about sustained turn -- a turn without loosing speed (and altitude).  This is in contrast to an instantaneous turn -- a turn where you are allowed to lose speed and/or altitude.
Peter Kämpf's answer addresses all the aspects of an instantaneous turn.  This is primarily a kinematic problem - i.e. the geometry of motion - not a lot to do with the airplane itself.  This means that the curves and behavior are the same for all airplanes for things like the relationship between turn radius, turn rate, and speed -- or turn rate, load factor (g's) and speed.
For an instantaneous turn, the two constraints are stall (CLmax and wing loading) and structure (max g's -- nmax).
However, for an instantaneous turn, you need to consider the specific excess power.  Largely determined by how powerful the engines are -- but also the weight of the aircraft and how clean you are (how little drag).
$P_s=\frac{V(T-D)}{W}$
$P_s$ Specific excess power
$V$ Airspeed
$T$ Thrust
$D$ Drag
$W$ Weight
$P_s$ is the energy maneuverability of the aircraft.  To maintain a sustained turn, you need to look at $P_s=0$.  Next, you need to dig into the drag...
$D=C_D\,q\,S_\mathrm{ref}$
$C_D$ Drag coefficient
$q$ Dynamic pressure $q=0.5\,\rho\,V^2$
$\rho$ Density of air
$S_\mathrm{ref}$ Wing reference area
We will assume a very simple form of a drag polar where the drag coefficient is made of a parasite and induced term...
$C_D=C_{D,0}+\frac{{C_L}^2}{\pi\,e\,AR}$
$C_{D,0}$  Parasite drag coefficient
$C_L$ Lift coefficient
$e$  Aerodynamic efficiency factor
$AR$  Aspect ratio
Finally, to look closer at the induced drag, we have to look at the lift coefficient.
$C_L=\frac{n\,W\,\cos(\theta)}{q\,S_\mathrm{ref}}$
This is a little different than a normal lift coefficient equation.
$n$ Load factor, how many g's are you pulling in the turn
$\theta$ Flightpath angle, if you're not climbing or diving, it is zero.  We will use this case.
OK, lets put it all together...
To have excellent sustained turn capability, you need to be able to maintain $P_s=0$ at the speed, altitude, and turn (load factor) that you desire.
You can achieve this with lots of thrust, minimal drag, and light weight.
$P_s=\frac{V(T-D)}{W}$
To minimize the drag, you need a clean airplane.  You first want the parasite drag to be a minimum.
$C_{D,0}$
But importantly, you also want the induced drag to be low.  This will tend to increase the aspect ratio (vs. an airplane not optimzied for sustained turn) and will have some other effects.
In fact, although we normally think about maximizing the lift-to-drag ratio of an airplane in cruise ($n=1$), for sustained turn, you want to improve the lift-to-drag ratio during the turn.
I believe the experimental Grumman X-29 was designed to hit best $L/D$ during a combat maneuver -- i.e. combat altitude, transonic speeds, and $n=3$ g's!


text:
PPL H - Previously logged hours from the past towards CAA and EASA after Brexit
I have 50+ student hours in rotorcraft from about 8 years ago in the UK under the CAA.
I am now looking to restart training in Europe for a dual EASA and CAA license.
I've been told that because my previous training was 'incomplete' the previous 50 logbook hours I have are not able to be credited towards these license applications.
Looking at EASA Part-FCL (FCL.035) they just state that the hours must be logged in the appropriate type, and do not mention the location, authority or time these must have been completed in.
https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf

Is my interpretation correct that flight hours for an EASA PPL can be credited from any time period at any location?

Did you try to send an email to the Local CAA of the country you are restarting training in?

I have not but I will do that to check, in Europe it seem like the country itself is not always the country issuing the license. I'll check with the country that would most likely be issuing the license.

Yes the instruction can (could) be carried out with any EASA CFI. Check with the country you want the license issued from

No response from the Authority I want to register in, and none from the one I want to train in either. Seems no one in any position of deciding, doesn't want to handle this question.

did you try asking other flight schools?